I would start with Castrol 20W50 for the first 500 miles or so. You are going to want to change the oil and filter after running it a bit, so why waste the money on synthetic that is going to be drained anyway. After the initial break in period, switch to the synthetic of your liking. I prefer Red Line, but that is a personal choice.
Some synthetic manufacturers specify conventional oil for the break in period, some don't.
On my race engines, we always break them in on the Dyno on conventional oil, and then switch to synthetic for the power pulls.
I hope I haven't muddied the water too badly.
Jeff